Electro-surgery is a method of using electric current to cut tissue. It is used for purposes such as removing lesions, controlling bleeding, or cutting tissue. Precise cuts can be made with limited blood loss. Electro-surgery is commonly used for in dermatological and surgical procedures. High frequency voltage, typically in the range of 400 kHz to 750 kHz is used in order to avoid stimulation of the nervous system which responds to low frequencies.
Electro-surgery is performed by connecting the electrosurgical blade or active electrode to an electrosurgical generator, activating the generator to supply current, and delivering the current through the blade and into tissue. A simple circuit is formed whereby current passes through the blade, into the tissue of the body, and out through another connection in the body such as a ground. The typical electrosurgical instrument is a metal blade with a very low level of resistance. The cell tissue has a high level of resistance. Due to the high resistance, heat builds up in the tissue causing individual cells to expand, explode, and burn away.
The blade is positioned in a pencil-like holder which the surgeon manipulates to achieve the desired effect at the surgical site. Selecting and adjusting the characteristics of the current delivered by the electrosurgical generator allows the surgeon to cut the tissue, to coagulate bleeding from the tissue, or to simultaneously cut and coagulate. The ability to control the application of electrical energy to the tissue to cut and coagulate tissue is one of the substantial advantages of electro-surgery, and such advantages contribute to the use of electro-surgery in most major surgical procedures.
The electrical power applied can vary from a few watts for delicate neurosurgical procedures to approximately 300 watts for cutting substantial tissues in open surgical procedures. The open circuit voltage prior to energy transfer into the tissue may be in the range of 5,000-10,000 volts peak to peak. The voltage drops substantially as the current flow increases through the highly resistive tissue. Typical tissue impedances range between about 10 ohms and 500 ohms.
The physical characteristics of a typical electrosurgical blade are important to carry out electro-surgery. The typical electrosurgical blade has two elongated broad, planar surfaces bisected by two narrow edges. The broad surfaces of the two broad sides are generally parallel and exist on opposite sides of the working area of the blade. The adjoining narrow edges extend between the broad sides and curve around a distal end or tip of the working area.
Cutting or coagulating is achieved by bringing the narrow edge into close proximity with the tissue. The current passes through the blade with little impedance and then through the narrow edge of the blade into the tissue. The narrow edges have a relatively small surface area causing high current Gaussian current density to flow through this area. The current is transferred into the tissue as relatively short arcs, thereby causing enough heat to explode or rupture the cells of the tissue at the interface with the narrow leading edge. The tissue separates at the leading edge leaving a well-defined incision. It is in this manner that the current from the electrosurgical blade cuts the tissue, rather than the tissue being separated from the physical contact and mechanical action of a sharp edge, as in traditional cutting procedures. The narrow edge of the typical electrosurgical blade is not sharp and cannot cut tissue as a result of mechanical action.
A significant drawback of the prior art is that blood and the innards of the bursting cells come in contact with and adhere to the surface of the electrosurgical blade. Although the impedance of the typically metal blade is far less than that of the tissue, it is still significant enough that the blade absorbs enough of the transferred energy to increase its temperature significantly during electro-surgery. The increased temperature of the blade causes the cell fluids, body fluids and blood to dehydrate, denature and accumulate on the blade in the form of a crust-like buildup. Unless periodically removed, the crust-like buildup increases as the blade is used. More particularly, charred and necrotized tissue and cells can be generated by localized excessive thermal heating, wherein such tissue and cells tend to adhere to the surgical instrument such as the cutting edge of a surgical knife. The presence of such tissue and cells on the working surface of the instrument interferes with subsequent cutting by disrupting the current field and correspondingly reduce the efficiency and efficacy of the instrument.
The crust-like buildup negatively affects the ability for the electrosurgical knife to function. To restore functionality the knife must be frequently cleaned. Doing so is only partially effective and is time consuming. Another alternative is to frequently replace the blades, but this adds cost and can also be time consuming. The buildup on the broad sides of the blade also has other negative consequences. The blade drags against the tissue at the incision and creates an undesirable “feel” when manipulating the instrument. Further, the crust obscures the ability for the surgeon to view the expected location of energy delivery from the blade into the tissue, decreasing the accuracy of the cut. These problem and consequences of the crust-like buildup on electrosurgical blades have been a long felt unsolved need in the art.
Various prior art methods have been devised in order to overcome the aforementioned problems by providing ways to minimize and remove the crust-like buildup. One approach in the art has been for the user to use a specifically-designed mechanical cleaning device into which the blade is inserted and withdrawn to scrape or otherwise remove the crust buildup. The mechanical scraping and cleaning techniques are generally not preferred by surgeons because scraping prolongs the surgical procedure. Moreover, scraping is generally not fully effective in removing all of the crust like material, but is better than doing nothing at all. Consequently, the necessity to scrape the blade during the surgical procedure has been tolerated by surgeons.
Another approach to avoid crust-like buildup on electrosurgical blades has been to coat the exterior of the blades with a nonstick coating. The nonstick coating minimizes the adherence of the crust-like materials. Since the broad sides of the blade attract the most buildup and are the primary location where the buildup normally occurs, it is ideal that the broad sides be coated. However, the narrow edges are primarily where the arcs of current flow from the blade to the tissue so it is important to have less or no coating on the narrow edges, so as not to impede the flow of current which would reduce the effectiveness of the device.
A variety of different types of release coating materials have been applied to electrosurgical blades. Among the types of release materials which have been used on electrosurgical blades are fluorinated hydrocarbon materials (similar to “Teflon”), silicone (polysiloxane), ceramic composites, paralyene polymers, and others. Among ceramic composites, thermally applied alumina (aluminum oxide—Al.sub.2 O.sub.3) or alumina composite such as alumina-chromia, magnesium oxide, zirconia-yttria, and zirconia-calcia, are all known in the art. A preferred ceramic coating has a dielectric strength of at least 1,000 volts/mm in the frequency range of 500 kilohertz to 1 megahertz, more preferably at about 3,000 volts/mm. These substances have been used on electrosurgical blades primarily because of their nonstick characteristics. Other factors which influence the choice of such materials for coating electrosurgical blades involve biocompatibility, heat resistance, dielectric strength, and adherence.
Adherence is a particularly important characteristic, because the nonstick, release material should remain on the broad sides of the blade, despite the relatively high temperature of the metal blade and the occasional electrical arcing from the broad sides to the adjoining tissue. Because of the desire for good adherence, the typical approach has been to mechanically roughen the metal body prior to applying the release or nonstick coating. Mechanically roughening the surface of the metal body increases the surface area of the metal body by creating a large number of mechanical peak and valley aberrations into an otherwise smooth surface. The increased surface area and the texture of the peaks and valleys provide a complex mechanical structure to which the coating material will adhere with increased tenacity. Typical mechanical roughening techniques involve grit blasting, etching, burnishing, or knurling. Another roughening technique is to fuse a layer of textured material to the smooth surface. The fused textured material causes the release coating to adhere.
While the roughened surface achieves the objective of enhanced adherence of the release material, it also creates certain undesirable characteristics. Each of the peaks of the roughened surface presents a minuscule elevated point source from which an electrical field gradient exists when the metal body of the electrosurgical blade is energized with high voltage. These elevated points decrease efficiency. Field gradients are responsible for initiating arcs of the electrical energy and should come only from the narrow sides or tip of the blade. The corners where the broad sides join the narrow edges create the desirable field gradient locations for the initiation of the arcs to deliver the energy for cutting and coagulating as described above. Arcing from the points of the roughened broad sides of the blade may have the tendency to destroy the nonstick or release coating material on the broad sides by erupting the coating from the points where the arcs initiate from the peaks. Once the nonstick coating is destroyed, a knife with a rough surface having many field gradients is less effective than a smooth knife having no coating to start.
To overcome the above-noted problems related to destruction of the non-stick coating and multiple field gradients, various prior art improvements function by providing thick or multiple coats of nonstick material to the blade. Once the coating has been built up to a sufficient thickness, enough electrical insulation exists to eliminate or inhibit the arcing from the broad sides. However, applying multiple coats of material to the blade increases its manufacturing cost and decreases the conductivity of the blade. The width of the blade between the coatings on the broad sides is also increased by the added width of the multiple layers of coatings. The increased width creates excess drag on the adjoining tissue as the blade cuts.
It is known from the prior art to provide an electrosurgical blade having a working area with a single uniform layer coating of nonstick, release material comprising substantially silicone (polysiloxane) initially applied over and adhered to both the broad and narrow sides of the device. In order to use the device, a drawback is that the user must vaporize or scrape off the coating initially present on the narrow edges and at the corners in the vicinity of the tip. During the vaporization or scraping process, the coating ideally remains intact and smoothly adhered to the broad sides of the electrosurgical blade, although the edges of the coating and electrical gradient at these edges may not be smooth.
The uniformity in the cross-sectional thickness of the coating will vary slightly on the narrow edges due to forces acting on a decreased area. Surface tension, fluidity, and quicker solidifying times reduce the thickness at those corners.
The crust buildup is a pitfall of the electrosurgical procedure. The crust spaces the blade from the tissue and makes it difficult to transfer energy into the tissue so as to achieve the desired electrosurgical effect. A typical area for the crust buildup is the broad sides of the blades because most of the energy transferred is through a narrow edge during cutting. The energy transfer tends to keep the narrow edges clean. Consequently, the buildup of crust is on the broad sides of the blades and is the impediment to conducting electro-surgery.